Reversing valve for hydraulic piston pump

ABSTRACT

A reversing valve for a hydraulic piston pump, including a pilot valve and a main valve. The pilot valve includes a pilot valve seat, a hollow spool and a pull rod. The main valve comprises an upper valve seat, a lower valve seat and a main spool. When the hollow spool is at a lower position, the control flow path communicates with the exhaust fluid flow path, and the main spool is at a lower position, so the power piston is driven to move upwardly by the power fluids provided by the main valve. When the hollow spool is at an upper position, the power piston is driven, by the power fluids provided by the main valve, to set at an upper position, and the power fluids provided by the pilot valve force the power piston to move downwardly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of International Application No. PCT/CN2018/000217 with a filling date of Jun. 7, 2018, designating the United States, now pending, and further claims to the benefit of priority from Chinese Patent Application No. 201710683380.7 with a filing date of Aug. 4, 2017. The content of the aforementioned applications, including any intervening amendments thereto, are incorporated herein by reference.

TECHNICAL FIELD

The present application relates to a hydraulic piston pump for extracting oil from wells, and more particularly to a reversing valve for controlling the reciprocating motion of the hydraulic piston pump.

BACKGROUND OF THE INVENTION

For existing hydraulic piston pumps, high-pressure power liquids are injected into wells by surface pumps, and sliding valves in the well controls the reciprocating motion of pistons at power ends, thereby driving the piston of the pump to reciprocate. As shown in FIGS. 1-2, a motor 101 drives a high-pressure plunger pump to suck a power fluid from a separator 103, and after pressurized, the power fluid is injected to a sliding reversing valve 120 and a piston motor 150 in a well via a power tube. Finally, the piston motor 150 drives an oil pump 160 to reciprocate to lift crude oils to the surface. In FIG. 1, 107, perforation section; 104, flowmeter; 105, pressure gauge; and 106, tube. In FIG. 2, 120, sliding reversing valve; 121, sliding reversing rod; 153, power piston; 151, power piston rod; and 163, pump piston. As a rodless oil production device, the hydraulic piston pump, having the advantages of high efficiency and high lift, is suitable for exploiting deviated and horizontal wells. Moreover, the temperature of the wellbore is kept by high-temperature power fluids to facilitate the flow of viscous oils and high pour point crude oils.

However, the existing hydraulic piston pumps adopt sliding valves to control the reciprocating reversing of the power piston, causing the following defects. Firstly, since the sliding reversing valve cannot reverse in a short stroke, the power fluids are required to have good lubricity to reduce the abrasion of moving members. Secondly, the engagement in the sliding reversing valve should be precise to avoid a jam of the sliding sleeve, so the power fluids are required to be finely filtered to ensure high cleanness. Thirdly, since members of the sliding valve is in clearance fit, the power fluids are required to have an appropriate viscosity; if the power fluids are selected from low-viscosity fluids, such as water, serious abrasion of the moving members and losses of the sliding valve will be caused. In the last century, crude oils are adopted as the power fluid of the hydraulic piston pump in worldwide oil fields, and specifically, the production fluid is used as the power fluid after dewatered, finely filtered and heated. However, when the water content in the oil well rises, high costs are caused since heavy work is needed to treat power fluids on the surface. By the end of the last century, due to high water contents in oil wells, the use of hydraulic piston pumps is significantly reduced in United States, and particularly, China adopts no hydraulic piston pump in oil wells for artificial lifts. Therefore, there is a desire for a hydraulic piston pump capable of using water or the production fluid in oil well as a power fluid in the field of mechanical oil recovery.

SUMMARY OF THE INVENTION

A reversing valve for a hydraulic piston pump is provided in the present invention, which aims to achieve the following objectives. Firstly, hydraulic piston pumps with such reversing valve adopt pure water or production fluids with a high water content as the power fluid, eliminating complicated devices and energy consumption for treating the power fluids. Secondly, such hydraulic piston pump is capable of working in a short stroke, greatly improving the reliability and endurance thereof. Thirdly, due to small leakage of the hydraulic piston pump, the efficiency is obviously improved and the energy consumption is reduced. Fourthly, compared to existing sliding reversing valves, the reversing valve of the present invention is in a lower cost.

In order to achieve above objectives, the reversing valve of the present invention adopts a structure with two two-position three way cone valves to replace the reversing valve of the existing hydraulic piston pumps. The reversing valve comprises a pilot valve and a main valve. The pilot valve comprises a pilot valve seat, a hollow spool, a pull rod and a sliding sleeve. A first seal ring and a second seal ring are provided on the pilot valve, and a third seal ring is provided on the sliding sleeve. A first seal line is formed at a junction between an upper end face and an inner surface of the pilot valve seat, and a second seal line is formed at a junction between a lower end face and the inner surface of the pilot valve seat. The hollow spool is provided with a first truncated cone and a second truncated cone. A first cylinder is provided above the first truncated cone, and a second cylinder is provided below the second truncated cone. A convex cylinder is provided on the second truncated cone, and a sealing cylinder is arranged on the convex cylinder.

The hollow spool is sheathed on the pilot valve seat and the sliding sleeve which are fixed in a pilot valve casing. The sealing cylinder of the hollow spool is movably engaged with an inner surface of the sliding sleeve, and an outer diameter of the sealing cylinder is equal to an inner diameter of the pilot valve seat. An upper end of the pull rod is provided with a trigger which is provided with a flow hole on a bottom, and a lower end of the pull rod is fixed at a top of an upper piston rod. The pilot valve is further provided with a high-pressure chamber, a control inlet port, a exhaust fluid inlet port, a power inlet port, a lower alternate flow path, a exhaust fluid flow path and a control flow path. A first annular flow path is formed between the hollow spool and the pull rod, and a second annular flow path is formed between an outer surface of the hollow spool and an inner surface of the pilot valve seat.

A damping flow path is formed between an outer surface of the convex cylinder and an inner surface of a lower end of the sliding sleeve. The damping flow path selects different flow areas according to different flow rates of a exhaust fluid, and the flow areas are 2-350 mm².

The main valve comprises an upper valve seat, a lower valve seat, an upper seal sleeve, a lower seal sleeve, a cylinder sleeve and a main spool which are arranged in a main valve casing. The main spool has a stepped shaft structure which is thick in a middle and thin at both ends. An upper truncated cone is provided at an upper end of the main spool, and a top cylinder is provided above the upper truncated cone. A lower truncated cone is provided at a lower end of the main spool, and a bottom cylinder is provided below the lower truncated cone. A middle cylinder is provided at a middle of the main spool, and an upper cylinder and a lower cylinder are respectively provided on upper and lower ends of the middle cylinder. A cross-sectional area of the middle cylinder is A; a cross-sectional area of the upper cylinder is B, and is equal to a cross-sectional area of the lower cylinder; a cross-sectional area of the top cylinder is C, and is equal to a cross-sectional area of the bottom cylinder, where (A-B)>B, so that the opening and closing of the main spool are controlled. A radial breathing hole and a vertical breathing hole are provided in the main spool. A throttle valve is arranged at a rear of the main spool and is made of cemented carbides or ceramics. A damping hole is provided on the throttle valve, and a diameter of the damping hole is 0.2-20 mm. Different diameters of the damping hole are selected according to structure parameters of the main valve.

A fourth seal ring is provided on the upper valve seat of the main valve, and a fifth seal ring is provided on the lower valve seat. A sixth seal ring and a seventh seal ring are respectively provided on outer and inner surfaces of the upper seal sleeve, and an eighth seal ring and a ninth seal ring are respectively provided on outer and inner surfaces of the lower seal sleeve. A tenth seal ring is provided on a main spool. The fourth, fifth, sixth, eighth seal rings are in a static seal, and the seventh, ninth and tenth seal rings are in a dynamic seal. A fixing nut is provided at the upper end of the main valve, and an outer layer is a tube. The main valve is provided with a power chamber, a first connection chamber, a second connection chamber, a exhaust fluid chamber, a breathing chamber, a control chamber, an upper power flow path and an upper alternate flow path. The power chamber communicates with the high-pressure chamber through the upper power flow path, the lower power flow path, the power inlet port and the first annular flow path. An upper end of the control flow path communicates with the control chamber, and a middle of the control flow path communicates with the control inlet port, and a lower end of the control flow path communicates with a lower working chamber of a power piston. An upper end of the upper alternate flow path communicates with the first connection chamber, and a middle of the upper alternate flow path communicates with the second connection chamber, and a lower end of the upper alternate flow path communicates with the lower alternate flow path communicating with an upper working chamber of the power piston. An upper end of the exhaust fluid flow path communicates with the exhaust fluid chamber, and a lower end of the exhaust fluid flow path communicates with the exhaust fluid inlet port and an annular space. The radial breathing hole and the vertical breathing hole are provided in the main spool. The vertical breathing hole communicates with a damping hole in communication with the exhaust fluid chamber and with the annular space via the exhaust fluid flow path.

When the power piston of a power end is close to a dead point of a power cylinder, the hollow spool is pushed to change positions by the trigger or a top of the upper piston rod, and set on the pilot valve seat under a hydraulic force, so that flow directions of a power fluid in respective flow paths are changed. Opening and closing positions of the main spool are controlled by the control inlet port, the control flow path and the control chamber of the main valve to change flow directions of a power fluid and a exhaust fluid, so that a moving direction of the power piston is controlled. In short, when the hollow spool is at an upper position, the control flow path communicates with the exhaust fluid inlet port, and a pressure of the control chamber is equal to a pressure of the breathing chamber. Since a pressure of the power chamber is larger than a pressure of the exhaust fluid chamber, the main spool is forced to locate at a lower position, which blocks the communication between the second connection chamber and the exhaust fluid chamber. The power fluid provided by the main valve passes through the upper alternate flow path and the lower alternate flow path to force the power piston to move downwardly. When the hollow spool is at a lower position, the power fluid enters the control chamber through the control inlet port and the control flow path. Since an upward resultant force applied on the main spool is larger than a downward resultant force applied on the main spool, the main spool is forced to set at an upper position. The power fluid provided by the pilot valve forces the power piston to go up in the power cylinder, and the power piston drives the pull rod to move. An initial action for the hollow spool is provided by the trigger on the pull rod and the top end of the piston rod, and the hollow spool is pushed to the reversing position.

During reversing, the reversing valve of the hydraulic piston pump of the present invention eliminates or reduces the vibration and impact of the main valve by providing the damper hole on the main spool, so that it can smoothly reverse under different operating conditions, thereby extending the service life of the reversing valve. The reversing valve adopts a structure with two two-position three way cone valves, and the valve seat and the valve spool are in a line seal, eliminating leakage during working. At the same time, since the valve spool will not be stuck due to impure power fluids, pure water or fluids with low viscosity and high water content can be directly used as power fluids, so that the need for power fluids with good lubricity, high cleanliness and appropriate viscosity is eliminated. On the other hand, the reversing valve is capable of reversing under a low pumping speed (less than 3 r/min), which greatly reduces the moving speed of moving members to reduce the abrasion, thus increasing the service life of the whole system. The above-mentioned advantages cannot be realized by the existing reversing valves of hydraulic piston pump.

The preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a surface installation and a down-hole pump of a hydraulic piston pump in the prior art;

FIG. 2 is a partial sectional view of the down-hole pump of the hydraulic piston pump in the prior art;

FIG. 3A is a schematic diagram of a reversing valve of a hydraulic piston pump according to the present invention;

FIG. 3B is a schematic diagram of the reversing valve showing connections of respective chambers and respective flow paths of the present invention, in which the reversing valve travels to a lower stroke of the hydraulic piston pump;

FIG. 3C is a schematic diagram of the hydraulic piston pump driven by the reversing valve of the present invention, in which the hydraulic piston pump starts the lower stroke;

FIG. 4A is a schematic diagram of the reversing valve showing connections of respective chambers and respective flow paths of the present invention, in which the reversing valve travels to an upper stroke of the hydraulic piston pump;

FIG. 4B is a schematic diagram of the hydraulic piston pump driven by the reversing valve of the present invention, in which the hydraulic piston pump starts the upper stroke;

FIG. 5 is a cross sectional view taken along line 5-5 in FIG. 3A;

FIG. 6 is a cross sectional view taken along line 6-6 in FIG. 3A;

FIG. 7 is a cross sectional view taken along line 7-7 in FIG. 3A;

FIG. 8 is an enlarged view of a pilot valve of the reversing valve of the present invention;

FIG. 9 is an enlarged view of a main spool of the reversing valve of the present invention;

FIG. 10 is a top view of the main spool of the reversing valve of the present invention; and

FIG. 11 is a cross-sectional view taken along line 11-11 in FIG. 8.

DETAILED DESCRIPTION OF EMBODIMENTS

It should be noted that FIGS. 3A and 3B are identical in view, except that components of the reversing valve are numbered in FIG. 3A, and chambers, inlet ports and flow paths are numbered in FIG. 3B.

As shown in FIGS. 3A and 8, a first seal line 13 a is formed at a junction between an upper end face and an inner surface of the pilot valve seat 13, and a second seal line 13C is formed at a junction between a lower end face and the inner surface of the pilot valve seat 13. The hollow spool 12 is provided with a first truncated cone 12 a and a second truncated cone 12 c. A first cylinder 12 b is provided above the first truncated cone 12 a, and a second cylinder 12 d is provided below the second truncated cone 12 c. A convex cylinder 12 e is provided on the second truncated cone 12 c, and a sealing cylinder 12 f is arranged on the convex cylinder 12 e. The pilot valve 10 further comprises a pull rod 17 and a sliding sleeve 14. A first seal ring 11 a and a second seal ring 11 b are provided on the pilot valve seat 13. A third seal ring 11 c is provided on the sliding sleeve 14. The hollow spool 12 is sheathed on the pilot valve seat 13 and the sliding sleeve 14 which are fixed in a pilot valve casing 18′. The sealing cylinder 12 f of the hollow spool 12 is movably engaged with an inner surface of the sliding sleeve 14, and an outer diameter of the sealing cylinder 12 f is equal to an inner diameter of the pilot valve seat 13 to ensure a balanced axial force of the hollow spool 12. An upper end of the pull rod 17 is provided with a trigger 15 which is provided with a flow hole 15 a on a bottom, and a lower end of the pull rod 17 is fixed at a top of an upper piston rod 51. As shown in FIG. 3B, the pilot valve 10 is further provided with a high-pressure chamber, a control inlet port 35, a exhaust fluid inlet port 36, a power inlet port 38, a lower alternate flow path 32, a exhaust fluid flow path 33 and a control flow path 34. As shown in FIGS. 8 and 11, a first annular flow path 39 is formed between the hollow spool 12 and the pull rod 17, and a second annular flow path 39′ is formed between an outer surface of the hollow spool 12 and an inner surface of the pilot valve seat 13.

A damping flow path 39 a is formed between an outer surface of the convex cylinder 12 e and an inner surface of a lower end of the sliding sleeve 14. The damping flow path 39 a selects different flow areas according to different flow rates of a exhaust fluid, and the flow areas are 2-350 mm².

The main valve 20 comprises an upper valve seat 23, a lower valve seat 23 a, an upper seal sleeve 26, a lower seal sleeve 26 a, a cylinder sleeve 27 and a main spool 22 which are arranged in a main valve casing 18 according to an order in FIG. 3A. As shown in FIGS. 9 and 10, the main spool 22 has a stepped shaft structure which is thick in a middle and thin at both ends. An upper truncated cone 22 a is provided at an upper end of the main spool 22, and a top cylinder 22 b is provided above the upper truncated cone 22 a. A lower truncated cone 22 c is provided at a lower end of the main spool 22, and a bottom cylinder 22 d is provided below the lower truncated cone 22 c. A middle cylinder 22 g is provided at a middle of the main spool 22, and an upper cylinder 22 e and a lower cylinder 22 f are respectively provided on upper and lower ends of the middle cylinder 22 g. A cross-sectional area of the middle cylinder 22 g is A; a cross-sectional area of the upper cylinder 22 e is B, and is equal to a cross-sectional area of the lower cylinder 22 f; a cross-sectional area of the top cylinder 22 b is C, and is equal to a cross-sectional area of the bottom cylinder 22 c, where a difference of A and B is set to be larger than B to control the opening and closing of the main spool 22. A radial breathing hole 43 and a vertical breathing hole 44 are provided in the main spool 22. A throttle valve is arranged at a rear of the main spool and is made of cemented carbides or ceramics. A damping hole 25 (shown in FIGS. 3B and 9) is provided on the throttle valve 24, and a diameter of the damping hole 25 is 0.2-20 mm. Different diameters of the damping hole 25 are selected according to structures parameters of the main valve 20.

A fourth seal ring 21 a is provided on the upper valve seat 23, and a fifth seal ring 21 d is provided on the lower valve seat 23 a. A sixth seal ring 21 b and a seventh seal ring 21 e are respectively provided on outer and inner surfaces of the upper seal sleeve 26, and an eighth seal ring 21 c and a ninth seal ring 21 g are respectively provided on outer and inner surfaces of the lower seal sleeve 26 a. A tenth seal ring 21 f (shown in FIG. 3A) is provided on a main spool 22. The fourth, fifth, sixth and eighth seal rings 21 a, 21 d, 21 b, 21 c are in a static seal, and the seventh, ninth and tenth seal rings 21 e, 21 g, 21 f are in a dynamic seal. A fixing nut 28 is provided at the upper end of the main valve 20, and an outer layer is a tube 29. As shown in FIG. 4A, the main valve 20 is provided with a power chamber 40, a first connection chamber 45, a second connection chamber 48, a exhaust fluid chamber 49, a breathing chamber 46, a control chamber 47, an upper power flow path 41 and an upper alternate flow path 42. Numeral 37 in FIG. 4A indicates an annular space. It should be noted that the upper power flow path 41, the lower power flow path 31 and the exhaust fluid flow path 33 are indicated by broken lines in the drawings, which is intended to explain the connection relationship between the respective chambers of the reversing valve, and actual positions thereof are shown in FIGS. 5-7. The power chamber 40 communicates with the high-pressure chamber 30 through the upper power flow path 41, the lower power flow path 31, the power inlet port 38 and the first annular flow path 39. An upper end of the control flow path 34 communicates with the control chamber, and a middle of the control flow path 34 communicates with the control inlet port 35, and a lower end of the control flow path 34 communicates with a lower working chamber 55 of a power piston 53. An upper end of the upper alternate flow path 42 communicates with the first connection chamber 45, and a middle of the upper alternate flow path 42 communicates with the second connection chamber 48, and a lower end of the upper alternate flow path 42 communicates with the lower alternate flow path 32 communicating with an upper working chamber 54 of the power piston 53. An upper end of the exhaust fluid flow path 33 communicates with the exhaust fluid chamber 49, and a lower end of the exhaust fluid flow path 33 communicates with the exhaust fluid inlet port 36 and the annular space 37. The radial breathing hole of the main spool 22 communicates with the breathing chamber 46 and the vertical breathing chamber 44. The vertical breathing hole 44 communicates with the damping hole 25 which communicates with the exhaust fluid chamber 49 and communicates with the annular space 37 via the exhaust fluid flow path 33.

In order to clearly illustrate the working principle of the reversing valve, this embodiment illustrates the reversing valve of the present invention based on the power end and pump of the A-type hydraulic piston pump (TRICO/KOBE Inc., US). Specifically, the reversing valve with the sliding sleeve in the A-type hydraulic piston pump is replaced with the reversing valve of the present invention, and other components at the power end and the pump are kept. FIGS. 3A and 3C are cross-sectional views of the A-type pump with the reversing valve of the present invention, in which the reversing valve starts the lower stroke. The A-type pump comprises a power end 50; where 51 is an upper piston rod; 51 a is a hollow portion 51 a of the upper piston rod 51. An oblique inlet port 51 b (shown in FIG. 3A) is provided on an upper end of the upper piston rod 51, and the hollow portion 51 a communicates with the high-pressure chamber 30 via the oblique inlet port 51 b. It should be noted that the lower end of the pull rod 17 is fixed with the top of the upper piston rod 51, so the pull rod 17 synchronously reciprocates as the upper piston rod 51 reciprocates. 52 a is a dynamic seal of the upper piston rod 51; 53 is a power piston; 54 is an upper working chamber of the power piston; 55 is a lower working chamber of the power piston 53; and 56 is a power cylinder. As shown in FIG. 3C, the A-type pump further comprises a pump assembly 60, where 61 is a power piston rod; 61 a is a hollow portion of the power piston rod 61; 63 is a pump piston; 64 is an upper working chamber of the pump piston 63; 65 is a lower working chamber of the pump piston 63; 67 a is an upper suction valve 67 a; 67 b is a lower suction valve; 68 a is an upper discharge valve 68 a; 68 b is a lower discharge valve 68 b; and 69 is a pump cylinder. 52 b is a dynamic seal of the power piston rod 61. A balance piston rod 62 which is provided with a hollow portion 62 a is further provided at a lower end of the pump piston 63 to ensure the balance of the force of the power piston 53 during reciprocating. The pump assembly 60 further comprises a dynamic seal 52 c for the balance piston rod 62 and a suction flow path 66. A balance communication hole 62 b is provided at a lower end of the balance piston rod 62 to connect the hollow portion 62 a with a balance chamber 62 c. The A-type pump further comprises a suction end 70. The annular space 37 and a perforation section 72 are separated by a packer 71, 73 is a pump intake, and fluids from an oil layer enter the lower suction valve 67 b and the upper suction valve 67 by passing through the pump intake 73 and the suction flow path 66.

Referring to FIGS. 3B, 8 and 3C, the first seal line 13 a of the pilot valve seat 13 is set on the first truncated cone 12 a of the hollow spool 12, so that the power fluid in the high-pressure chamber 30 is sealed. At the same time, the control chamber 47 communicates with the exhaust fluid inlet port 36 via the control flow path 34, the control inlet port 35, the second annular flow path 39′ and the damping flow path 39 a. Due to the damping flow path 39 a, flow resistance of the exhaust fluids is generated, which forces the hollow spool 12 to move upwardly and keeps the hollow spool at an upper position. At this time, pressures in the breathing chamber 46 and the control chamber 47 of the main valve 20 are the same, which are the pressure from the exhaust fluid. Lower and upper end faces of the spool 22 are subjected to the pressure from the exhaust fluid and the power fluid. Since the pressure of the power fluid is much larger than the pressure from the exhaust fluid, the main spool 22 is in a position shown in FIG. 3B. The high-pressure power fluid from the power chamber 40 enters the first connection chamber 45, and then enters the upper working chamber 54 of the power piston 53 through the upper alternate flow path 42 and the lower alternate flow path 32 to push the power piston 53 to move downwardly in the power cylinder 56. At the same time, the exhaust fluid in the lower working chamber 55 is forced to enter the control flow path 34, and then is discharged into the annular space 37 through the control inlet port 35, the second annular flow path 39′, the damping flow path 39 a and the exhaust fluid inlet port 36 of the pilot valve 10, and finally the exhaust fluid, together with production fluids, is lifted to the surface. As shown in FIG. 3C, when the power piston 53 goes down, the power piston rod 61 drives the pump piston 63 goes down in the pump cylinder 69. At the same time, the upper suction valve 67 a and the lower discharge valve 68 b are opened; and the lower suction valve 67 b and the upper discharge valve 68 a are closed. Thus fluids in well enters the upper working chamber 64, and the fluids in the lower working chamber 65 is discharged into the annular space 37 and is lifted to the surface.

As shown in FIG. 4, when the power piston of a power end is close to a lower dead point, the upper piston rod 51 drives the trigger 15 on a top of the pull rod 17 to force the hollow spool 12 to move downwardly, so that the second seal line 13C of the pilot valve seat 13 is seated on the second truncated cone 12 c of the hollow spool 12. At this time, the high-pressure chamber 30 communicates with the second annular flow path 39′, and the second annular flow path 39 is disconnected with the exhaust fluid inlet port 36. After the power fluids from the power chamber flow out of the control inlet port 35 through the power inlet port 38 and the first annular flow path 39, the power fluids are separated into two ways. One way of the power fluids enters the control chamber 47 of the main valve 20 through the control flow path 34. Since an upward resultant force applied on the main spool 22 is larger than a downward resultant force applied on the main spool 22, the main spool 22 is forced to be at a position shown in FIG. 4A. At this time, the power chamber 40 and the first connection chamber 45 are separated, and the second connection chamber 48 communicates with the exhaust fluid chamber 49, so that the lower alternate flow path 32 communicates with the exhaust fluid chamber 49. At the same time, the other way of the high-pressure power fluid from the power chamber 40 enters the lower working chamber 55 of the power piston 53 through the lower end of the control flow path 34, and the power piston 53 is forced to go up, and then the exhaust fluid of the upper working chamber 54 is forced to enter the second connection chamber 48 through the lower alternate flow path 32, and then is discharged into the annular space through the exhaust fluid chamber 49 and the exhaust fluid flow path 33, and finally, the exhaust fluid together with the production fluid is lifted to the surface. As shown in FIG. 4B, when the power piston 53 moves up, the power piston rod 61 drives the pump piston 63 to move upwardly. At this time, the upper discharge valve 68 a and the lower suction valve 67 b are opened; and the lower discharge valve 68 b and the upper suction valve 67 a are closed. The fluids in the well enters the lower working chamber 65 of the pump, and the fluids in the upper working chamber 64 of the pump is discharged to the annular space 37, and is then lifted to the surface.

When the power piston is close to the upper dead point, the hollow spool 12 is pushed by the upper piston rod 5 to move upwardly, so that the connections of the flow paths are changed, which causes changes of pressures in the respective chambers of the main valve 20. Then, the main spool 22 is forced to return to the positions shown in FIG. 3A. Next, the power piston 53 is driven to move downwardly again.

The above is only one embodiment of the reversing valve of the present invention in a double-acting hydraulic piston pump, and this embodiment is not intended to limit the reversing valve of the present invention. The reversing valve of the present invention can be used to design various hydraulic piston pumps including double-acting pumps, single-acting pumps and ultra-high lift piston pumps with multiple power pistons. Moreover, reciprocating piston pumps driven by down-hole electric rotary hydraulic pumps can also be designed by adopting the reversing valve of the invention. It should be noted that any hydraulic piston pumps based on the principles of the reversing valve of the present invention shall fall within the scope of the present invention. Any modifications and changes can be made to the reversing valve without departing from the principles of the present invention, which shall fall within the scope of the present invention. 

We claim:
 1. A reversing valve for a hydraulic piston pump, comprising: a pilot valve; and a main valve; wherein the pilot valve comprises a pilot valve seat, a hollow spool, a pull rod and a sliding sleeve; a first seal ring and a second seal ring are provided on the pilot valve seat, and a third seal ring is provided on the sliding sleeve; the pilot valve seat and the sliding sleeve are provided in a pilot valve casing; the hollow spool is sheathed on the pilot valve seat and the sliding sleeve, and is provided with a sealing cylinder; the sealing cylinder is movably engaged with an inner surface of the sliding sleeve; an upper end of the pull rod is provided with a trigger which is provided with a flow hole on a bottom, and a lower end of the pull rod is fixed at a top of an upper piston rod; the pilot valve is further provided with a high-pressure chamber, a control inlet port, a exhaust fluid inlet port, a power inlet port, a lower alternate flow path, a exhaust fluid flow path and a control flow path; a first annular flow path is formed between the hollow spool and the pull rod, and a second annular passage is formed between an outer surface of the hollow spool and an inner surface of the pilot valve seat; the main valve comprises an upper valve seat, a lower valve seat, an upper seal sleeve, a lower seal sleeve and a cylinder sleeve which are arranged in a main valve casing; a fourth seal ring is provided on the upper valve seat, and a fifth seal ring is provided on the lower valve seat; a sixth seal ring and a seventh seal ring are respectively provided on outer and inner surfaces of the upper seal sleeve, and an eighth seal ring and a ninth seal ring are respectively provided on outer and inner surfaces of the lower seal sleeve; a tenth seal ring is provided on a main spool; the fourth, fifth, sixth, eighth seal rings are in a static seal, and the seventh, ninth and tenth seal rings are in a dynamic seal; a fixing nut is further provided on the main valve; the main valve further comprises the main spool having a stepped shaft structure which is thick in a middle and thin at both ends; a radial breathing hole and a vertical breathing hole are provided in the main spool; a throttle valve is arranged at a rear of the main spool and provided with a damping hole; the main valve is provided with a power chamber, a first connection chamber, a second connection chamber, a lacking liquid chamber, a breathing chamber, a control chamber, an upper power flow path and an upper alternate flow path; wherein the power chamber communicates with the high-pressure chamber through the upper power flow path, the lower power flow path, the power inlet port and the first annular flow path; an upper end of the control flow path communicates with the control chamber, and a middle of the control flow path communicates with the control inlet port, and a lower end of the control flow path communicates with a lower working chamber of a power piston; an upper end of the upper alternate flow path communicates with the first connection chamber, and a middle of the upper alternate flow path communicates with the second connection chamber, and a lower end of the upper alternate flow path communicates with the lower alternate flow path communicating with an upper working chamber of the power piston; an upper end of the exhaust fluid flow path communicates with the exhaust fluid chamber, and a lower end of the exhaust fluid flow path communicates with the exhaust fluid inlet port and an annular space; when the power piston of a power end is close to a dead point of a power cylinder, the hollow spool is pushed to change positions by the trigger or the top of the upper piston rod, and is set on the pilot valve seat under a hydraulic force, so that flow directions of a power fluid in respective flow paths are changed; and opening and closing positions of the main spool are controlled by the control inlet port, the control flow path and the control chamber of the main valve to change flow directions of a power fluid and a exhaust fluid, so that a moving direction of the power piston is controlled.
 2. The reversing valve of claim 1, wherein the hollow spool is provided with a first truncated cone and a second truncated cone; a first cylinder is provided above the first truncated cone, and a second cylinder is provided below the second truncated cone.
 3. The reversing valve of claim 1, wherein the hollow spool is provided with a convex cylinder; the convex cylinder and the inner surface of the sliding valve form a damping flow path which has a flow area of 2-350 mm².
 4. The reversing valve of claim 1, wherein an outer diameter of the sealing cylinder is equal to an inner diameter of the pilot valve seat.
 5. The reversing valve of claim 1, wherein an upper truncated cone is provided at an upper end of the main spool, and a top cylinder is provided above the upper truncated cone; a lower truncated cone is provided at a lower end of the main spool, and a bottom cylinder is provided below the lower truncated cone.
 6. The reversing valve of claim 1, wherein the main spool has a middle cylinder and an upper cylinder, and a difference of a cross-sectional area of the middle cylinder and a cross-sectional area of the upper cylinder is larger than the cross-sectional area of the upper cylinder.
 7. The reversing valve of claim 1, wherein a diameter of the damping hole ranges from 0.2 mm to 20 mm. 